Automatic gain control circuits as utilized in radio receivers are well known in the art, and in general are circuits utilized to automatically vary the amplification of a signal being processed by the receiver in accordance with the changing strength or intensity of the signal at the input to the receiver to provide a substantially constant output power for large variations of signal strength at the input to the receiver. The automatic gain control circuit, in one aspect, consists of a means for taking, at the detector of the receiver, a voltage proportional to the strength of the incoming carrier signal being processed by a receiver and applying the same as a bias to an intermediate frequency amplifier of the receiver to reduce the gain of the intermediate frequency amplifier as the voltage proportional to the incoming signal being processed increases. In another aspect, the "Q" of a portion of the circuit in an intermediate frequency amplifier of a receiver may be varied by utilizing the voltage proportional to the incoming carrier signal being processed by the receiver to vary the Q of the particular circuit.
Typical prior art automatic gain control circuits utilized components such as electrolytic capacitors and ceramic capacitors which types of capacitors are not suitably fabricated by state of the art integrated circuitry. In the aforementioned prior art circuits, the direct current component of a detected intermediate frequency signal, representative of the radio frequency strength of the incoming signal, is utilized to control the collector current of the intermediate frequency amplifier, which reacts with an overload diode to lower or increase the Q of a tuned circuit in the intermediate frequency amplifier. Lowering of the Q of the tuned circuit in the intermediate frequency amplifier by the prior art leads to degradation of the received signal.